Separation of hafnium from zirconium



May 31 1960 l.. G. ovERHoLsER ETAL 2,938,769

SEPARATION OF HFNIUM FROM ZIRCONIUM 2 Sheets-Sheet l Filed July 3l, 1952mw -Nm Bmx iNvl-:NToRs Char/es J. Baramr. Bv y/e 6. Over/roher@Joh/:241g Ramsey ATTUEA/Y May 31, 1959 L. G. ovERHoLsER ET AL 2,933,769

SEPARATION OF HAF'NIUM FROM ZIRCONIUM 2 Sheets-Sheetl 2 Filed July 31,1952 msm,

John W Ramsey Wwf/#iw ATTaeA/Y United States I arent tice 2,938,169Patented May 3l, 19,60

SEPARATION or HAFNIUM FROM zrRcoNIUM Filed July 31, 1952, Ser. No.301,902

' 3 Claims. (Cl. 23-23) Our invention relates to an improved process forpurify-ing zirconium and more particularly to the removal of hafniurnimpurity from zirconium values. f

The hafnium content of zirconium ores varies from about 1% to about 54%by Weight with an average of `about 3%, Zirconium and hafnium havealmost similar chemical propertim, and for this reason it has been foundextremelydiiiicult to eifect their separation, .even after considerableprocessing and purification. Thus, commercially availablezirconium metaland zirconium compounds .usually-contain from about 1% to about 2%hatnium `by weight. For most industrial applications, this material maybe utilized with satisfactory rults. However, in certain instances, itis necessary to employ an extremely pure grade of zirconium,particularly zirconium which is substantially hafnium-free. For example,the presence of only a few tenths of a percent of hafnium renderszirconium unsuitable for use as an internal structural material inneutronic reactors due to hafniums unusually high neutron absorptioncross-section, whereas substantially hafnium-free zirconium is eminentlysatisfactory for this purpose.

Numerous methods have been used to separate hafnium from zirconium.These methods have included fractional crystallization or precipitation,ion-exchange, fractional distillation of relatively volatile compounds,electromagnetic separation, thermal diffusion, preferential extraction,electrochemical separation, and differential decomposition of salts.However, these methods either required excessive repetition of steps toobtain the required separation, or were unadaptable to economicallyfeasible large scale production, i.e., production involving tonnagequantities of substantially hafnium-free zirconium.

One of the more promising of these prior art methods, was disclosed byW. Fischer and Walter Chalybaeus in Z. Anorg'. Chem. 255, 79-100 (1947),and 255, 277-286 (1948). The object of this method was to preparezirconium-free hafnium rather than halfnium-free zirconium and comprisedsubstantially the following preferred procedure: An aqueous phasecontaining zirconium and hafnium yas suifates, ammonium thiocyanate,and, in a few instances, ammonium sulfate, was contacted with diethylether in which thiocyanic acid had been dissolved. The hafnium ispreferentially extracted into the organic phase.

ln view of their desire to prepare only small quantities of enrichedhafnium, Fischer et al. did not further process the slightlyhafnium-depleted aqueous phase containing relatively large quantities ofzirconium, but rather recycled the `hafnium-enriched organic phase tofurther remove zirconium and, thereby, further enrich the hafnium. Thus,no suitable method was presented for obtaining zirconium even remotelyapproaching the substantially hafnium-free condition as would berequired, for example, in a neutronic reactor. Furthermore, the lowsolubility of zirconium in sulfate solutions would have constituted anextremely'seious obstacle to any high rate of production of hafnium-freezirconium.

Furthermore, we .find that the certain critical ranges and combinationsof process conditions described hereinafter for producing substantiallyhafnium-free zirconium differ significantly from the conditionsdescribed by Fischer et al, for the production of. ha-fnium low inzirconium content, and that numerous unusual process modifications arenecessary to insure the feasible production of commercialquantitiesofhafnium-free zirconium. In addition, the preferred solventused by Fischer et al., ydiethyl ether, is excessively volatile,somewhaty soluble in water and relatively expensive'. Also, thiocyanicacid decomposes in diethyl ether' at a rate which, in addition to theabovefdisadvantages, makes this solvent especially 'unsuitable for largescale operations. Fischer et al. tried to solve certain of thesedisadvantages by using other solvents.v vButyl alcoholbutyl acetate anddi-N-propyl etherV were tried but little or no separation was achieved.

- An object of your invention, therefore, is to provide a process forsubstantially completely removing hafnium impurity from zirconium.

Another object of our linvention is to provide an economicallyfeasible,v continuous, plant scale process for separating zirconium fromhafnium.

Another object of our invention is to provide 'an organic solvent in theherein described process which is superior to prior art solvents withrespect to Vzirconiumhafnium separability, volatility, cost, Watersolubility, and thiocyanic acid-organic phase stability.

till another object is to produce zirconium ofsuiciently high purity andresulting lowA neutron absorption cross-section to permit its use inneutronic reactors.

Other objects and advantages of ourV invention-*will be apparent fromthe following description.

Inaccordance with our invention, -hafnium may be substantiallyquantitatively removed from zirconium on a largerscalel by a processwhich comprises contacting an acidic -aqueous phase containing solublehafnium and zirconium values -together with chloride-ions with'arsubstantially water immiscible ketone solvent phase, at least onej ofsaid phases containing thiocyanic acid, separating the'resulting organicphase from the resultingV of only a few individuals and represents aunique andY significant technological advance over the art procedureshereinidentiiied.

Employing our process, the hafnium content of commercial quantities ofzirconium may be Vreadily reduced, in a safe, continuous, andeconomically feasible manner, to the strikingly low amount of about 100parts per million and with about a 96% overall plant yield of zirconium.

Furthermore, We nd that a critical arrangement of the numerous processvariables as hereinafter discussed results in an unusual degree ofstabilization of our process solutions as compared to the lack ofstability .noted by Fischer et al. in their preferred process and,therefore, contributes vmaterially to the success of our continuousprocess. v v

In general, we find that substantially Water immiscible organic ketonesolvents are suitable for use with our invention. Satisfactory resultsmay be achieved, for example, utilizing such ketone solvents as hexone(methyl isobutyl ketone), methyl n-amyl ketone, methyl n-hexyl Iketone,methyl isopropyl ketone and ethyl butyl ketone.

:many prior Numerous significant advantages, some of which appearentirely unpredictable,result from our discovery that ketones aresignicantlys'uperiorz to othersolvents` as employed in theproc'es'sle'rein described, particularly whenV employed'in conjunctionwithchloride ions. Substantially all of the disadvantages of theprior-art solvents` are overcome. Thus, ketones are less volatile,cheaper in the case-of hexone, .less soluble inwaterand'resultin asmaller rate of decomposition of thiocyanicacid, as compared to thediethyl ether preferred. inV the` process of :Fischer et al. Theseadvantages for ketones are con-V siderably further enhancedby thediscovery that vbetter separation factors rcan .be `achieved than withdiethyl; ether when using the optimum conditions herein described. Astill'f'rther advantage'is vthat ketones are unusually amenable to arecyclinglstepas` hereinafter described, since we find that metalcationsimay be readily stripped from ithe ketones, ,while substantiallyall the thiocyanicacid remains, Ythe resulting ketone-thiocyanic acidphasebeing satisfactorynfor` direct reuse. Process costs are therebymaterially lessened. In addition, we find that the ketones, bythemselves, may be advantageously employedv forg'recovering thiocyanatevalues at suitable stages in our process.;v jr Y K In view of theavailability of commercial quantities of hexoney and its .superiority'overother ketones in our process,- our invention'will befurtherillustrated specifically with respect lto hexone j 1 Y We note ,thatwhilehexoneis vent, some decompositionlofithiocyanic acid dissolvedtherein still Ytakes place, whereas in butyl acetate, which yields :aconsiderablydowe'r, degree. of-separation @of hafniumrfromK zirconium,4there is very slight decomposition ofthio'cyanicacid. We'have foundthat an'inpredictable stabilization of thiocyanic acid appears to resultwhen approximately? 20% Vto .approximately 25% butyl acetate` lbygvolumeis addedto hexone, the separation factor remaining `substantially.unaffected. This rangegaPPearfS tofbefcritieal since, with less butylacetate,

less resistance todecompositionis noted, while with Vmore,

butyl'acetate, theseparation factor was signicantly decreased., However,for largegscale production, we still prefertoA utilize'only hexone,vsince vit is found more e- .cienttoA merely Ycontinuously separate thesmall amountv o f decomposition'products by such conventional means asYa filter press rather l than suffer the inconvenience ofvhandling'twosolvents instead of one.

When,- employing any, of the `solyentsor solvent combinations taughtherein, although not critical, suitable ratiosl of organictoqaqueous-.phase'in a batch or continuby far preferred sol- Yapproximately l,

We find that the presence of a suitable' quantity of freeacidfin theaqueous phase is necessary toachieve outstanding results. In thisrespect, mineral acids are suitable. However, HNO3 introduces theldisadvantage of reacting with thiacyanate, and H2804 limits thesolubility of zirconium in solution` due to the low solubility ofZr(SO4)2 as already discussed.VV HC1 and HClO.,l are considered moresuitable than any of the otheracids Yfor large scale operation and,in'view'offits lower'cost, hydrochloric acidis greatlypreferred-.The useof hy' drochlorie acidV greatly favors theV 'extractionof both zirconiumand hafnium and vappears to contribute signicantly to the stability ofVthe aqueous phase, iQe. preg vents hydrolysis and subsequentprecipitation of metal ions, to a degree not attainable'vvithrY otheracids. This stability is particularly vital to` aA plantvscalecontinuous process wherein large volumes of solution must traverselengthy passages. Y

' We find that the adverse effect ofthe sulfate anion Vin the priorartprocess herein discussed, added either as'an acid or a neutral-compoundnsuch as=(NH)2SO4 or Zr(S.O,)2, on zirconium Y solubility. andthe' degree of extraction, may be overcome to an unexpected degree byusing a system containing bothjsulfate and chloride.

The solubilitylimt may be significantly: raised, although stillYconsiderably lower .than Vin the sulfate-freey chloride system, whilethe separation factor is improved kover the sulfateffree chloridesystem. Although excellent results are attainable withjsuchavcombination system, we still Y chloride anionsV may be Vemployed incertain combina-f aqueousacidic solutions, may behafnium-decontaminatedV in accordance Ywith our process. are, for,example,` ZrOClz, ZrCl4, Zr(OHY)4, and Zr(ClO4)4.j However, it`islpreferred to,v add thev zirconium in the form of ZrCl4'orZrOCl2ZrCl4 and ZrOCl-3 are relatively; highly soluble under thepreferred extraction conditions, permittinga highrate ofproduction,particularly vin acontinuousprocess, as compared to the.highest achievable productionrrates' using other less soluble zirconiumcompounds. `In addition-,the chlorides contribute a portion of thechloride ion con- Y centration which we prefer to employ inour process.

vWhen employing relatively solublefzirconium com- Y pounds such as ZrCl4or ZrOClz, suitable concentrations Suitable compounds a concentration ofabout preferfoi continuous plant scale operation,"the extreme Ysimplicity of the sulfate-free Achloride system which merely requires alarger number of theoreticalextraction stages to achieve theV samedegree of separation at a much higher rate`; of iproduction of,substantially hafnium-free zir-A conium.

However', in the laboratory, where long lcolumns are of hydrochloricacid are from'about 0.5 molar to, aboutV Y2 molar .Y whilela'concentration of about l vmolar is preferred. If it is desired toemploy a sulfate-chloride sys-J tem,'suitaole Vconcentrations of sulfateanionto be added to the vabove chloride concentrations are from'about,0..0l, molar` to about l molar while a concentration of`approxi-y mately 0.5 molar is preferred. f

- It is noted from previous discussions that sulfate andtionsinlthefaqueous phase ofour system. There isrno criticalityjasrtothe manner in whichthey are Vaddedlas- Y long Yasthe desired range. ofitotal concentration of any single anion is achieved. Thusyin aYsulfatechloride system,{sulfate maybe added, forv example, Zr(SO4)2,-(NH4)2SO or H2894, while the chloride may be added, for example as ZrCl4or ZrOCl2,-AorI-1Cl. however, in the vsulfate-chloridel system, to Vaddchloride ions in the form of ZrOClzor ZrCl4l and HCl and sulfate anionsAas (NH4)2SO4. j-

Y Thiocyanic acid may initially beV added-"to either the' aqueous phase,the organic phase, or both. When added to only one phase, a suiiicientlyconcentration must be provided to result in suitable equilibriumconcentration ofV thiocyanate vin both phases during the Aextractionprocedure.Vv However, itis generally preferred to add' aqueous phase arefrom about l molar to about 3 molar whilefa concentration of'V about2.5. molar .is preferred. Similar .concentrationsV are applicable Atothe organic phase. VIt preferred to include thiocyanic vacid vin theaqueous phase AviaV theV compound'lfII-ISCN (the Ahydrojv Itispreferred,

gen cation being provided by HC1 or H2804 as herein described), whilethiocyanic acid may be introduced into the organic phasepby extractionof thiocyanic acid from an aqueous acidic solution of thiocyanate valuesas will be apparent in the following description. y

Employing the reaction conditions as 'set 4forth in precedingparagraphs, zirconium, in a multi-stage batch process, usually rangingfrom approximately v6 to 12 stages, may be substantiallyfreed fromhafnium impurity. However, any .process without recovery and recycle Yofvarious` valuable'reagents such as thiocyanate and hexone would .berelatively costly to operate. We have dis.- covered methods ofaccomplishing such recoveries and recycles which edect a'many-foldreduction in operating expenses. p

Thus, we have discovered thatva simple stripping of the hafnium-enrichedthiocyanate-containing organic phase resulting from the basic organicextraction step of our process, with a suitable concentration ofsulfuric acid, serves to quantitatively remove hafnium from the organicphase with only a small loss of thiocyanate values, thus permittingrecirculation of two costly vprocess items. This is an important factorin making continuous, countercurrent plant operation possible.

Thus, for the latter purpose, suitable concentrations of sulfuric acidin aqueous solution are from about 2 normal'to about 6 normal while aconcentration of about 4 normal is preferred. Suitable ratios of theaqueous sulfuric acid phase to the organic phase are from about l partaqueous to about 3 to 5 parts organic, while about 1 part aqueous toabout 4 parts organic is preferred.

Any valuable amounts of thiocyanate values remaining in thehafnium-containing aqueous ed'luent from the sulfuric acid scrubbingstep may be recovered `by a simple hexone extraction, and the resultinghexone-thiocyanate phase may then be combined With the other recycledhexone-thiocyanate phase.

For purposes of process efciency and prevention of build up ofimpurities in the system, the thiocyanate-containing organic eiuentremaining from the sulfuric acid scrubbing step may be split into twostreams, one being recycled as already indicated, to the extractionstep, the other being processed in a thiocyanate recovery system toseparate thiocyanate values Afrom the organic solvent, thereby providingfor recycle of pure thiocyanate to the aqueous feed material. In thethiocyanate recovery system, the thiocyanate-hexone solution may beneutralized with ammonium hydroxide and the resulting two phases allowedto separate. The thiocyanate ions are quantitatively extracted from thehexone by .this procedure, into the aqueous phase. The resultingthiocyanate-free organic solvent may then be utilized to recover theremainder of the thiocyanate values employed in our process which appearin the zirconium enriched aqueous product eiuent from the zirconiumextraction step.

We nd that the thiocyanate values in this eiuent may be readilyrecovered merely by scrubbing same with thiocyanate-free hexone obtainedfresh or from the thiocyanate recovery system just described. Theresulting lthiocyanate-containing organic phase may then be re-employedin the zirconium extraction step. For thus recovering thiocyanatevalues, suitable ratios of organic to aqueous phases are from about lpart organic to about 1-3 parts aqueous, while a ratio of 1 part organicto 2 parts aqueous is preferred.

We have also discovered that process efliciency may be considerablyimproved by stripping the hafnium enriched thiocyanatecontaining hexoneefliuent from the extraction step, prior to the sulfuric acid scrubbingstep, with an aqueous hydrochloric acid solution. We iind that suitableconcentrations of hydrochloric acid will preferentially strip a portionof the extracted zirconium from the `already hafnium-enriched hexonephase and the resulting zirconium-containing hydrochloric acid strippingsolution can be admitted directly to the extraction step at the feedpoint. The latter .solution is found to contain an unexpectedly `lowamount of hafnium, usually not -'appreciably greater than the -hafniumcontent of the'zirconium plant feed material. Water alone is alsosuitable for stripping purposes but hydrochloric acid is more eliicientand is'preferred, especiallysince it is desired to introducehydrochloric acid anyway 4into the feed material, as heretoforeindicated. Suitable concentrations of hydrochloric acid in water lforstripping purposes are from about 0.5 molar `to about 4 molar whilea'concentration of approximately 3.5 molar -isrpreferred. Suitable ratioof stripping `solution to organic phase are from about 1 part strippingsolution Vto'about 4 parts to about 9 parts organic while a ratio of -1part stripping to about 7 parts organic is preferred. Y

Since the hydrochloric acid requirements for the zirconium feed streamare supplied from the hydrochloric acid stripping column, no additionalhydrochloric acid need 4be added to the feed whenthe disclosed hydrochloric acid recycle is employed'. V'In fact,1.the optimum strippingconcentration of hydrochloric acid (3.5 normal) may be too high foroptimum 'extraction of zirconium Vfrom the feed and it may becomedesirable to partially neutralize the feed stream with an alkalinereagent, .preferably ammonium hydroxide. It is noted that when zirconiumtetrachloride is employed, its hydrolysis in water contributes evenadditional free acid to the system. We nd that an improvement in theprocess may be achieved by adding approximately 1 mole of ammoniumhydroxide for each mole of zirconium present before extraction, thuskeepingthe-hydrochloric acid concentration in the extraction step withinthe preferred range herein specified. t

Although the temperature is -not critical to the success of our process,we iind that the separation factor is roughly inversely proportional tothe temperature. Thus a decrease in operating temperature results in anincrease in separation factor; it is therefore desirable to operate atroom temperature or at lower temperatures, and the separation factor ismarkedly improved by operation in lthe 0 C. to 5 C. range. v

We find, using the preferred reaction conditions, that the time requiredfor equilibrium to be reached is less than 30 seconds. Therefore, and inview of other advantages herein discussed, any suitable type of appara-tus for enabling intimate contact of continuous streams ofsubstantially immiscible liquid phases may be employed.. The apparatusmay comprise, for example, a continuous mixer-settler system, a simplebatch mixing and separating system, or a continuous, countercurrentcolumn system. The latter system is preferred and is hereinafterdescribed.

The following is a brieiiy summarized description of a preferredembodiment of our invention. The separation is preferably carried out incolumns in a continuous countercurrent manner. VColumn sections forextraction, stripping, scrubbing and thiocyanate recovery may ybeemployed either combined in one -column or in a multicolumn system.

Zirconium tetrachloride or oxychloride containing hafnium impurity isdissolved in water and the required quantities of ammonium thiocyanateand ammonium hydroxide are added to form the extraction feed solution.Feed solution is continuously pumped to an extraction column section.Hexone-thiocyanic acid solution is continuously pumped into the bottomof the extraction column countercurrent to the feed solution, andha'fnium is preferentially extracted thereby. The'resulting hafnium andthiocyanate containing hexone from the extraction column tiowsAcontinuously into the stripping column, countercurrent to a continuousflow of a stripping solution of dilute hydrochloric acid. The resultingaqueous hydrochloric acid stripping solution containing strippedzirconium is continuously fed into the lextraction'ccllumn with the feedsolution. The stripped hexone 'containing ..7 u verypure hafnium owsinto the scrubbing column Where thefha'fnium islvremoved by. scrubbingWithv a sulacidjsolu'tiodn. 'l`his hexone; free ofmetal, butv stillcontaining thiocyanic acid isfrecirculated to the extraction column. i ii "8 10.and into pump head tank 11, from whence the filtered hexone is.returned to; the bottom of extraction column 4 by ppoft'iningpump'andrecycle linef'28, while lline 24 is employed to carrytlie remainingvportion of scrubbed hexone to a thiocyanatey recovery system described`herein .(not shown); 2 j 1 j flna` preferred operation of' theVYapparatus just described', fzirconiumchloride, NHrSCN, including make-up'NH4'SCN jfro'm .thel .thiocyanate recovery system (not shoyvnL'andY,NH4OH -are added in suitable portions to feed make-up tankl. 'Iheresulting solutionis discharged rthrough line 12,'pumped /thr'oughilterpress 2 bypurnp v 27, and vreceivedlby feedstorage tank `3 through line13.

.Ravvhexoneto be fed to the thiocyanate recovery column is preparedfroma .portionhof the sulfuric acid' scrub hexone dvsftsdto. :a thipyanaterecovery .systemeformmonium neutralization as herein. described.VAmmonium thiocyanat'e from this system is used in Yfeed, make-up.

. .Substantially Yhafniumfree zirconium solution iscontinuouslyvrernovelvfrom the extraction column and may be processedinto the desired final form by conventional procedures. l Y n Y .4

A suitablegvsubstantially continuous system forelecting a preferred`embodirwncutV-of our invention is illustrated diagrammatically in theaccompanying drawing. 1

In greateru .d etail and-,referring to the drawing, tank .1, is provided.for making up feed solution,.and is sup'- pliedatthebottom-.with;liquid.discharge line. 12 from Y which feedlsolution ,isforcedA through .filter press 2 by centrifugal pump 27. Tank 3 isprovided to storerltered solution received fromrilter press `2, throughline 13, and

'is' supplied at the( bottom with liquid outlet line 14.

n Columnfl is provided for contactingV the aqueous and hexone phases andis lsupplielat the top with aqueous freedvsolutionfrom feed storage tank3 byline 14 and proportioning pump 37. Line 1S and centrifugal pump 30serve-to transfer the aqueous solution from thebottom of extractioncolumn 4 to the top of recovery column 5 which is provided to recoverthiocyanate values therefrom. Proportioning pump V38 and line 29 areutilized to introduce fresh hexone (source not shown) into the bottom ofrecovery column 5 and line 16 is employed to transfer the hexone phasefrom the top of recovery col- .umn 5to the bottom ofextraction column 4.Recovery column 5 is supplied with naqueous phase product exit lineV276. f

Stripping column., 6Yis employed Vfor stripping, of its zirconiumcontent,` the hexone received .at the bottom from the top of extractioncolumn 4 via line 17. Line 19 communicates lWithfthe top of -column;.6and supplies hydrochloric acid strippingrsolution" (source not shown) asmetered by proportionate pump .41. The bottom of column 6is suppliedwith exitlinelS which, in cooperation with centrifugal pump 31,Vvtransfers aqueous hydrochloric acid solution Iused for strippingpurposes in column 6, from the bottom of column 6 to the top'ofextraction-'column 4. YValves 33, 34, andY 42 and centrifugal pumpY32.are provided to side-pass a portion of the liquid .from line 18,through filter pressv7, Vand backto line 18. lColumn 6. is also providedat the top with Waste exit line .which serves to carry stripped hexoneto the bottomof. scrubbing column 8, the .latter being furnished toscrub the hexone entering from line 20 .of extracted.impurities,rprimarily. hafnium.v Line communicates )with theV top of'.column V8 and supplies the aqueous HzSO,L scrubbing solution (source notshown) as metered by proportioning pump 39. VLine 22 is employed toremove scrubbed hexone from lthe top of column 8 and is divided intolines 23 and 274;'line 23 vbeing employed to carry a. portion of theyscrubbed hexone to storage tank 9.

' Column, discharge line 35 and centrifugal pump 36 are .utilizcdtoprocess the organic solvent through lter press .Feed 'solution'isrcontinuously released Yfrom feed storage .tanllinto' discharge line 14and continuously metered into the top o f. extraction column 4 by pump37. i f ,concurrently a suitablequantityf of hydrochloric acidsolutionisfcon'tinuously adrnxed, by means of line 18 troni/the bottomofstripping column. 6, With the feed vsolution..enteringthe top ofncolumn 4. The hydrochloric i acid solutionV also includesanyV zirconiumsalvaged in the str'ippingcolur'nri'as hereinafter described.Meanwhile',

hexonethiocyanicv acid Vsolution is continuously fed into the bottom ofcolumn 4 from the, top of column 5 by solvent line 16 and fromsolventrecycle line 28 as continuou'sly.metered4 by vpump 40 from head tank1,1. The

hexone. continuously ascends (column 4,A contacting thecontinuouslyfdscendirig ,aqueousy phase, and preferenf ,tiallyextracting hafniurn therefrom.v .Ther'esultingzirconium enrichedaqueousvphase continuously removed from the .bottom of extraction column4 and transferred to the upper portion of thiocyanate reco'very column 5by means of line v15 and pump-30. Raw hexone .received from thethiocyanate recovery system (not shown) is continuously fed into thebottom of column Strom hexone feedline 29--by pump 38 and continuouslyascends column 5, contacting the continuously descendinghafnium-depleted aqueous phase, recovering HSCNtherefrom,.and beingremoved at the top vby means of solvent Yfeed line 16. The resultingaqueous phase containingv substantially hfnium-free zirconium Yproductis continuously removed from the bottom of column 5 through line 26-stored,`for subsequent conversion to v ny. desired hafnium-freezirconium compounds o r zir.- coniummetal. Y Y Y Concurrently, hafniumenrichedhexone is continuously transferred from` the top of columnY 4 to.the bottomV of Y strippingA column `6 Ythrough `line 17 andcontinuously Ythrough line 20 andin ascending column 8 -is stripped ofitsh-afnium content by a continuously descending aqueous H2SO4 solutionsupplied at the top of column 8 by pump 39 and scrubbing solution.supply line 25,. the resulting hafnium-'containing sulfate solutionbeingremoved from the bottom of column 8 by means of line 21. v The hexone.phase, containing thiocyanate, is continuously removedfrom the top ofcolumn 8 by line. 22, and is split into two streams, line 24vcarryingone stream'to thevthiocyanate recovery system, and line-23 carrying theother stream to storagetank 9 for subsequent removal by line and pump 36to filter press 10,Y and eventual reuse Vinthe extractionv` step asalready described. Y

A mixer-settler 'type of apparatus ma ralso be employed in a manneranalogous to the operation'of the column system just described. Thegeneral mechanism of conium solution is passed .countercurrent to anextracting solvent. The aqueous phase containing zirconium is'introduced to a mixing chamber at the bottom While the solvent isintroduced at the top. -Ar driven stirrers mix the two phases, and the'mixtures pass through center outlets to settling chambers. Here thephases separate and advance to subsequent mixing Achambers in oppositedirections.

The following specific examples illustrate our invention in greaterdetail. y

' EXAMPLE I.

ln the apparatus illustrated diagrammatically in Fig. `l, 4 inchdiameter Pyrex glass columns-wereemployed, usi'ng the system describedin our preferred embodiment, under the following conditions land withthefollowinglresults.'

Length of columns (total):

Extraction (3 columns) 180 ft. Stripping (2 columns) 125 ft. scrubbing(l column) 6 5ft. Y Thiocyanate recovery (1 column) f 55 ft. Hexone rate140 g.p.h. SCN concentration in recycle hexone v'2.7 molar.' HC1 rate,stripping section 18-'20 g.p.h. HC1 concentration 3.5' molar. SCN,concentration in 0.0 molar. SCN, concentration out 2.5-3.0 molar. Feedrate, zirconium oxychloride solution 50 g.p.h. HCl concentration 1molar. HSCN concentration 2.6 molar. Zr concentration V1 lb./gal. H2504rate, scrubber solution 35 g.p;h- H2804 concentration normal. SCN conc.,feed to thiocyanate re- Y p covery column 1.60 molar. SCN conc.,discharge from thiocyanate recovery column 0.1 molar. SCN conc., hexoneto column 0.0 molar. SCN conc., hexone from column 2.50 molar. Rate ofhexone to thiocyanate recovery'column 40 g.p.h. Rate of aqueous solutionin column 70 g.p.h. Conc. Hf in raw feed 1.5-2.0%. Conc. Hf in productZr 100 p.p.m.

Conc. Zr in product Hf ripproximatelyl 2%.

Yield of Zr product based on feed Operation of the extraction units iscarried out to achieve the best balance between product purity and yieldof zirconium. Increased purity of zirconium can be obtained at theexpense of yield and hafnium purity. With our method of operation, itispossible to obtain a yield of better than 96% of zirconium containingabout 100 ppm. hafnium while obtaining hafnium product containingbetween 0.5% and 3.0% zirconium.

Even greater separation and production rates may be achieved byincreasing the length and diameters of the columns, respectively, andproportionately increasing rates of ow of process liquids.

Only one column, containing superimposed al1 the functions of themultiple column herein described, would be suitable for the operation ofour invention. However?, for greater compactness, protection 'frombreakage, and easier access for maintenance repair work, the breakdownof process functionsfinto -separatecolumns ispreferred andan even largernumwberof still shorter column sections may be utilized, ifpdesired. Inaddition, the column and associated apparatus may be constructed out ofmaterial other than glass, such as suitable plastics or corrosionresistant metal.

The following is an example illustrating by a laboratory test thecriticalness of the percentage composition andthe satisfactory behaviorof a 25 butyl.acetate75% hexone mixture (whichwe have describedherein asresulting in a `signicantreduction in the decomposition of thiocyanate).

Table I EXTRACTioN 'rEsTs 25% 50% Composition ot Butyl Butyl- .100%Organic Phase 'Hexone Acetate, Acetate, Butyl 75% 50% Acetate HexouevHerone Percent Hf Extracted 93 l90 8O Percent Zr Extracted.-- -r 27`-204 l5 7 Separation Factor 34 3o 23 13 The` decomposition ofthiocyanate, noted in heXone alone,.is substantially completelyeliminated. The above and additional results show that, although theluseof a'pl proximately 20% to approximately25% butyl'acetateby volumein hexone in place of 100% hexone as the organic solvent in ourhafnium-zirconium solvent Yextraction process does slightly reduce Atheextraction of both hat nium and zirconium fromthe aqueous phase intovtheorganic phase, the separation Vfactor remains substantially thesame.

EXAMPLE `Ill v Example III illustrates theV use of sulfatein Ythe feedmaterial. The mixer-settler apparatus of Fig. 2"was utilized. Thefollowing conditions were employedV in six Vmixer-settler stages plus 2extra stages of mixing..and settling in which the hexone was broughtinto countercurrent contact with 25% sulfuric acid. The sulfuric acidremoved the dissolved ymetals (zirconium and hafnium) from the solventand left most of the thiocyanic o acid so that the hexone could then bereused.

The hafnium content of the feed, based on zirconium, was 1.5%.

Aqueous Phase Organic Phase scrubbing Solution 0.2 molar ZrCh Hexonecontaining 25% Hrs O4.

2.0 molar HSCN.

2.0 molar added HCl.

0.75 molar (N H4)2SO4 Flow rate 150 ce./ Flow rate 15 min. cc./min.

1.75 molar NHlSCN.

Flow rate 25 cc./min.

Under these conditions the product aqueous solution was substantiallyfree of hafnium.

In general, it may Vhe said that-fthe above examplesaremerelyillustrative and should not' be construed as limiting the'scope ofour invention. Any metal cation which com'- plexes with rthir'icyanatemay be separatedVv using systems such asherein described. Furthermore,numerous reagent recycle variations and, combinations are kvpossiblewithin the scopey of the foregoing description; Thus, Athe scopeofmy'inven'tion should be understood to' be limitedjonly as indicated bythe appendedclaims. s

VWeclaim: j

l. An improved solvent "extraction process 'for Veffecting substantiallyquantitative. separation'jrof hafnium impurities from zirconium valueswhich comprises contacting an aqueousl feedV solution l'phase,containing zirconium, hafniuin, and V'chloride values,"with a methylVsobutyl ketone phase, atl least Tone of said phases containingYthiocyanate values,v separating the. resulting yzirconium enrichedaqueous phase from the Yresulting |hafniumfenrichedmethyltisobtylketone, .contacting said hafiu enriched methyl isobutylketone with anVaqueous/ hydrochloric acid'solution, separating the resultingzircomum-containing hydrochloricV acid solution from the resultingzirconium-depleted, hafnium-enrichedmethyl isobtyl ketone, andacidifyingsaid feedsoltion with Ythe resulting zirconium-containing hydrochloricacidV solution. 2. The process of claim 1 wherein thezirconium-depleted'hafnium-enriched methyl sobutyl ketone is contactedwith an aqueous sulfuric acid solution, .the resultinghafnium-containingsulfuric acid solution is separated I.

from the resulting thiocyanate-containing methyl sobutyl ketone, and theresulting thiocyanate-containing methyl sobutyl vketone iscontactedwith,fresh feed solution.W

3. `An improved solvent extraction process for eiecting substantiallyquantitative separation of hafnium impurity. fromzirconium values whichcomprises'preparing an aqueous feed solution-approximately 0.2 molar Vto`approximately 1.5 molar in hafnium-containing zirconium tetrachloride,approximately 2 molar to approximately 5 molar in ammonium thiocy'anate,continuously acidifyiing V`said feedsolution to rapproximately v0.5 toapproximately.2molar inhydrochloric acid, `continuously con- Y tctingthe resulting acidied feed solution with a countereurrent streamlofmethyl sobutyl ketone containing approximately 2 molar to approximately5 molar thiocyanic acid, at aV flowl ratio 'of approximately 3 partsto-approxi-Y mately 9 parts of Ymethyl sobutyl ketone` toV about 1 partaqueous phase, continuously kseparating the resulting VVzircon'iumenriched thiocyanate-containing laqueous phase A Vto abouti 1` partVto-fabout 3 parts aqueous phase vand continuously :separating theAresulting thiocyanate-containing methyl sobutyl ketone` from the;resulting thiocyanate-free zirconium enriched aqueous phase,Vcontinuouslycontacting fresh portions of said acidied feed solutionwith a countercurrent stream of :the resulting Y essere@ Tns 12`thiocyanate-contaii ning methyljsobutyl ketone, continus.,ouslycontactingfsaid hafm'um |enriched thiocyanate-con; taining'methyl'.isobutyl' ketone.` with a countercnrrent' stream of an vaqueoussolution approxirifatelyl 2 'molar' 5 to l'approximtely V3,5 ,molarfin'hydrochloric acid at a new rateirafieifasofl pan amaai-.elution 'teabout 4 partsto ab'iit"9"partsmethyl"sobutyl ketone, con:l

Vtinuously` separatingthe y resulting zirconium-containing hydrochloricacid lsolutionV from the resulting zirconiumsobutyl ketone,continuously" ac'idifying said feed solution with theresultingZirconium-containing hydrochloric acidVK solution, continuouslycontactingl the zirconiumdepleted thiocyanate-containinghafnium-enrichedmethyl sobutyl Vketone -vvith a countercurrent ow of approxi- Vmately 2molar to approximately 7 molar aqueous sulfurie acid solution at a ow'ratio. kof approximately 1 part aqueous to about 3v parts Yto about 5Yparts methyl Vsobutyl ketone, continuously separating the resultinghafnium-,containing su1furic`facid solution'rfrom the resultingthiocyanate-containing methyl sobutyl ketone, continuouslycontactingiaprtionof said thiocyanatecontaining methyl sobutyl 'ketonewith( a" countercurrent stream of fresh feed slution,'continuouslyneutralizing 25 the remaining portion of said thiocyanate-c'ontainingmethyl isobutyllketone `with ammonium hydroxide, continuouslyseparatingthe resulting ammonium thiocyanate- `containing aqueous phasefrom the resulting thiocyanatefree methyl sobutyl ketone, continuouslycontacting'said zirconium-enriched thiocy'anate-containing aqueous phasewith thiocyanate-free methyl isobutyl'ketone and continuously employingsaid 'aqueous' thiocyanate solution in vthepreparationjof,saidfeedsolution. 'i

References Citedin the offthis patent i. i

' UNITED-,STATES PATENTS 2,227,833 Hixsonlet a1, Jan. 7; 1941 2,578,623Asselinet al. `.Q ..I -Dec. l1, 1951 o OTHER' REFERENCES Leaders et al.;U.S. Atomic'Energy' Coiim'tissio'n declassied'Paper No., YA-5597, Feb.Yl,V 1950, declassied Nov. 18, ,1955, 31 pages., Available ,fromv Oice`of Technical Services, Dept. of Commerce, Washington V25, D.C. Price2512?.A i

Weinhardrtet al.: Industrial and Engineering Chemistry, vol. 43, No. 7,pages 1676-1684 (1951). Y*

Morton: Laboratory Technique in Organic Chemistry, pages 198, 199(1938), vpublished bytMcGraw-Hill Book Co., N.Y. l j v Fischer et al.:Zeitschrift fr anorganische Vund All- (1947);'and vol. 255, pages277-286 depleted thiocyanate-containing hafnium-enr'iched methyl UNTTEDSTATES PATENT OFTTCE CERTIFICATE 0F 'CURECTION Patent No 2,1938q769 May3l@Y 1960 Lyle Go Overholser et al It is herebjr certified that errorappears in the-printed specification of the above numbered patentrequiring correction and that the said Letters Patent should reed ascorrected below.

Column 7U line 559 for "proportionate" read propor- Signed and sealedthis 4th day of April 1961 (SEAL) Amst; ERNEST W. SWTER ARTHUR W.cRocKER

1. AN IMPROVED SOLVENT EXTRACTION PROCESS FOR EFFECTING SUBSTANTIALLYQUANTITATIVE SEPARATION OF HAFNIUM IMPURITIES FROM ZIRCONIUM VALUESWHICH COMPRISES CONTACING AN AQUEOUS FEED SOLUTION PHASE CONTAININGZIRCONIUM, HAFNIUM, AND CHLORIDE VALUES, WITH A METHYL ISOBUTYL KETONEPHASE, AT LEAST ONE OF SAID PHASES CONTAINING THIOCYANATE VALUES,SEPARATING THE RESULTING ZIRCONIUM ENRICHED AQUEOUS PHASE FROM THERESULTING HAFNIUM HYRICHED METHYL ISOBUTYL KETONE, CONTACTING SAIDHAFNIUM ENRICHED METHYL ISOBUTYL KETONE WITH AN AQUEOUS HYDROCHLORICACID SOLUTION, SEPARATING THE RESULTING ZIRCONIUM-CONTAININGHYDROCHLORIC ACID SOLUTION FROM THE RESULTING ZIRCONIUM-DEPLETED,HAFNIUM-ENRICHED METHYL ISOBUTYL KETONE, AND ACIDIFYING SAID FEEDSOLUTION WITH THE RESULTING ZIRCONIUM-CONTAINING HYDROCHLORIC ACIDSOLUTION.